The shift register is used for controlling the operations of a plurality of adjacent circuit in the field of digital circuit. For example, the shift register is an important unit used in a source driver in display panels. The thin-film transistor (TFT) process is widely used in products with display panels because integrated circuits can be realized on a glass substrate in a display panel with the TFT process.
The source driver and the shift registers therein can also be realized with the TFT process. However, the characteristic parameters of a TFT are different with the preset characteristic parameters because of the process variation or being used for a long time. With in all the variations, the most important one is the variation of the threshold voltage (VTH) of a TFT. Regarding a shift register, the variation of the threshold voltage of a TFT may result in the fact that certain transistor switches in the shift register are not turn off as expected. As a result, the voltage level of the output signal of the shift register would vary and the shift register suffers from extra power dissipation due to the current leakage.